The invention relates to a fluidised-bed apparatus, for example a boiler for the combustion of coal in the form of fluidisable particles in a fluidised bed, in which there is a tube arrangement forming part of a heat exchanger with the fluidised bed and an additional air or gas blowing network which is independent of the fluidisation air or gas network.
Fluidised beds with heat exchangers are already known, in particular in the field of boilers. A known exchanger comprises at least two headers, one at the fluid inlet and one at the fluid outlet, between which the heat-exchange tubes are located. Various arrangements of these exchange tubes between the headers have been proposed. Horizontal tubes have a larger area of contact with the fluidised bed than vertical tubes, but they are highly susceptible to erosion and corrosion. Vertical tubes withstand erosion better than horizontal tubes and inclined tubes; they require a larger number of tubes, but they also possess the advantage of providing a greater degree of flexibility as regards operation since, by varying the height of the fluidised bed, it is possible to alter significantly the depth of immersion of these tubes in the fluidised bed. A particularly convenient method for varying the height of the fluidised bed consists in regulating its expansion by changing the fluidisation speed by means of an additional-air blowing network which is independent of the main fluidisation-air network.
The main object of the invention is to provide, in a simple manner, a fluidised-bed apparatus which has a heat exchanger with vertical tubes and an additional-air blowing network and with which it is possible to obtain all of the abovementioned advantages, in particular flexibility in operation and a low degree of erosion or corrosion of the tubes.